The present disclosure relates to light emitting diode (LED) illuminating devices and methods, and more particularly, to LED-based light bulb solutions in a format akin to a common incandescent light bulb or lamp. As a point of reference, the terms “bulb” and “lamp” are used interchangeably throughout this specification.
Incandescent light bulb or lamp replacement solutions, such as compact fluorescent lights (CFLs) and LED bulbs, are becoming more widely used as the cost of energy increases. Unfortunately, aesthetic concerns exist for the “tubes” of the CFL format, and unusual shapes of many LED environmental solutions. Consumers and commercial concerns have existing fixtures or sockets that in many cases look unappealing with these new replacement bulb offerings. In many cases, consumers avoid doing what is environmentally and financially correct to maintain the appearance of the common incandescent bulb.
LED-based lights provide the longest lasting, and over time the lowest cost and most environmentally-friendly, solution for lighting. Two major problems have been the high initial cost per lumen and the directionality of the light emitted by LED bulbs. More recently, greatly improved LED-based bulb devices have been developed, arranging a number of individual LEDs relative to a bulb structure otherwise highly similar in appearance to a conventional incandescent light bulb (e.g., A-19 format). Several highly promising bulb devices incorporating this format are described in U.S. Pat. No. 8,013,501, the entire teachings of which are incorporated herein by reference. With these and similar designs, the bulb device is intended to be used with a conventional incandescent light bulb fixture or socket (delivering AC power from a power source). The bulb device carries or includes appropriate circuitry that converts the AC power at the fixture or socket to power appropriate for powering or driving the LEDs. The LEDs generate heat that must be removed. In this regard, the small size of the LED die emits substantial heat per unit area from the back of the LED package. LED bulb or lamp designs typically use relatively large metal heat sinks to transfer this heat to surrounding ambient air.
LED light bulb designs involve a complex set of tradeoffs between the selection and numbers of LED components, LED drive parameters, system thermal constraints, system lifetime and performance targets. All of these tradeoffs are made within limits of cost goals and a desire to approximate the appearance of a conventional incandescent bulb. Implementation difficulty increases with the luminosity output requirements of high watt equivalency solutions.
Design of power conversion systems to meet light output targets of 60 W, 75 W, 100 W equivalency will be increasingly challenging, requiring careful selection of components, circuit board design and thermal design. Transfer of system heat from both the conversion electronics and the LEDs is particularly challenging. Internally mounted LEDs and power conversion components must be mounted on substrates providing thermal paths where heat is conducted to external surfaces for convective transfer.
A related heat transfer issue in the realm of LED-based light bulb design is the heat transfer paths and related surface systems. Any acceptable design must transmit the heat in a manner that also avoids electronic hazard paths. Regulatory compliance safety testing includes subjecting the lamp to a series of very high transient voltages and confirming that the lamp design does not allow such events to reach human accessible surfaces in such a way as to pose a safety issue to users.
LED-based light bulb designs give rise to multiple heat transfer-related concerns. Any resolution of these problems will be well-received.